Sound-absorbing material with excellent sound-absorbing performance and method for manufacturing thereof

ABSTRACT

The present invention provides a sound-absorbing material with excellent sound-absorbing performance and a method for manufacturing thereof. More particularly, it relates to a sound-absorbing material, which can improve sound absorption coefficient and transmission loss by forming large surface area and air layer, so as to induce viscosity loss of incident sound energy, may make light-weight design possible because it can express excellent sound-absorbing performance even using reduced amount of fiber, and can improve sound-absorbing performance by using binder fiber having rebound resilience, so as to maintain enough strength between fiber and also to maximize viscosity loss of sound energy transmitted to fiber structure; and a method for manufacturing thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase application filed under 35 USC 371of PCT International Application PCT/KR13/008630 filed Sep. 26, 2013,which claims the benefit of Korean Patent Application No.10-2012-0108764 filed on Sep. 28, 2012, the entire contents of which areincorporated herein by reference.

BACKGROUND

(a) Technical Field

The present invention relates to a sound-absorbing material withexcellent sound-absorbing performance and a method for manufacturing thesame. More particularly, it relates to a sound-absorbing material withexcellent sound-absorbing performance, which can be used for blockinginflow of external noise into vehicle interior by being attached asvehicle components or interior and exterior materials of a vehicle body,and can be used in electric devices and the like that use motor parts soas to improve noise insulation performance thereof

(b) Background Art

In general, noise introduced into a vehicle may be classified into anoise generated at an engine and introduced through a vehicle body and anoise generated when tires are contacted with a road surface andintroduced through a vehicle body. There may be two ways to block thesesnoises such as improving sound-absorbing performance and improving noiseinsulation performance. Sound-absorbing means that generated soundenergy is converted into thermal energy and then dissipated while it istransmitted through internal route of a material, and noise insulationmeans that generated sound energy is reflected and blocked by a shelter.

According to such characteristics of sound, in order to improve Noise,Vibration & Harshness (NVH) of a vehicle in general, a heavier andthicker sound-absorbing material has been mainly used in luxury cars.However, when such sound-absorbing material is used, noise may bereduced, but there is a problem of deteriorating fuel efficiency byincreasing vehicle weight.

Further, in order to overcome problems of the conventionalsound-absorbing material, a method in which porosity of the material isimproved by thinning fiber thickness have been developed therebyimproving sound-absorbing performance and also reducing weight of fiberaggregate. However, this method may also have a weakness such that needssurface density of the fiber aggregate may be improved in order toimprove the desired NVH performance.

Further, in order to manufacture non-woven type fiber aggregate, staplefiber and binder fiber are mixed together at a proper ratio. As thebinder fiber, in general, staple fiber manufactured byconjugate-spinning regular polyester is used for an inner layer and lowmelting polyester is used for an outer layer.

However, when using this conventional binder fiber with the low meltingpolyester, the fiber aggregate is hardened, and thus there may be aproblem that vibration generated by sound wave propagation andtransmitted to matrix structure is not fully attenuated, therebyreducing sound absorption coefficient mainly at low frequency region.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve theabove-described problems associated with prior art.

The present invention is objected to provide a sound-absorbing material,which may improve sound absorption coefficient and transmission loss byforming large surface area and air layer, so as to maximize viscosityloss and dissipation route of incident sound energy, and makeslight-weight design thereof possible because it can realize excellentsound-absorbing performance even using reduced amount of fiber; and amethod for manufacturing thereof

Further, the present invention is objected to provide a sound-absorbingmaterial, which may improve formability as well as maintain enoughstrength between fiber, and may have improved rebound resilience,thereby ultimately having excellent vibration attenuation capabilityagainst sound energy transmitted inside matrix; and a method formanufacturing thereof

To achieve the above objects, in one aspect, the present inventionprovides a method for manufacturing a sound-absorbing material thatcomprises forming fiber aggregate in a nonwoven fabric form, and thefiber aggregate comprises:

a non-circular shaped fiber satisfying the following Formula 1; and

a binder fiber that partly binds a plurality of the non-circular shapedfibers.

$\begin{matrix}{1.5 \leq \frac{P}{\sqrt{4 \times \pi \times A}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

(A: Fiber cross sectional area (μm²), P: Circumference length of fibercross section (μm))

In a preferred embodiment, the sound-absorbing material may bemanufactured by using the non-circular shaped fiber satisfying the valueof the Formula 1 of 2.6 or greater.

In another preferred embodiment, the sound-absorbing material may bemanufactured by using the non-circular shaped fiber satisfying the valueof the Formula 1 of 3.0 or greater.

In still another preferred embodiment, the non-circular shaped fiber maybe at least one selected from the group consisting of six-pointed starshape, 3-bar flat type, 6 leaf type, 8 leaf type and wave type.

In yet another preferred embodiment, the non-circular shaped fiber maybe 35 to 65 mm in length.

In still yet another preferred embodiment, the binder fiber may comprisea low melting (LM) elastomer having elastic recovery modulus of 50 to80%, and rebound resilience rate of the sound-absorbing material may be50 to 80%.

In a further preferred embodiment, the binder fiber may be conjugatedfiber which is conjugate-spun by using the LM elastomer as onecomponent.

In another further preferred embodiment, the LM elastomer may be atleast one selected from the group consisting of a polyester-basedpolymer, a polyamide-based polymer, a polystyrene-based polymer, apolyvinylchloride-based polymer and a polyurethane-based polymer.

In still another further preferred embodiment, the LM elastomer may bemanufactured by esterification and polymerization steps using dimethylterephthalate(DMT) and dimethyl isophthalate(DMI), or terephthalicacid(TPA) and isophthalic acid(IPA) as an acid ingredient(Diacid), and1,4-butanediol(1,4-BD) and polytetramethyleneglycol(PTMG) as a diolingredient (Diol).

In yet another further preferred embodiment, the sound-absorbingmaterial may be manufactured by using the non-circular shaped fiber of50 to 80 wt % based on the total weight of the sound-absorbing materialand the binder fiber of 20 to 50 wt % based on the total weight of thesound-absorbing material.

Further, in another aspect, the present invention provides asound-absorbing material, which may comprise: a non-circular shapedfiber satisfying the following Formula 1; and a binder fiber whichpartly binds a plurality of the non-circular shaped fibers.

$\begin{matrix}{1.5 \leq \frac{P}{\sqrt{4 \times \pi \times A}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

(A: Fiber cross sectional area (μm²), P: Circumference length of fibercross section (μm))

In a preferred embodiment, the non-circular shaped fiber may satisfy thevalue of the Formula 1 of 2.6 or greater.

In another preferred embodiment, the non-circular shaped fiber may be atleast one selected from the group consisting of six-pointed star shape,3-bar flat type, 6-leaf type, 8-leaf type and wave type.

In still another preferred embodiment, the non-circular shaped fiber maybe 35 to 65 mm in length.

In yet another preferred embodiment, the non-circular shaped fiber maybe 1.0 to 7.0 De in fineness.

In still yet another preferred embodiment, the binder fiber may comprisea LM elastomer having elastic recovery modulus of 50 to 80%, and reboundresilience rate of the sound-absorbing material may be 50 to 80%.

In a further preferred embodiment, the binder fiber may be conjugatedfiber which is conjugate-spun by using the LM elastomer as onecomponent.

In another further preferred embodiment, the LM elastomer may be atleast one selected from the group consisting of a polyester-basedpolymer, a polyamide-based, polystyrene-based polymer, apolyvinylchloride-based polymer and a polyurethane-based polymer.

In still another further preferred embodiment, the sound-absorbingmaterial may comprise the non-circular shaped fiber of 50 to 80 wt %based on the total weight of the sound-absorbing material and the binderfiber of 20 to 50 wt % based on the total weight of the sound-absorbingmaterial.

In yet another further preferred embodiment, the non-circular shapedfiber may satisfy the value of the Formula 1 of 3.0 or greater.

Hereinafter, terms used in the present invention will be described.

The term “wave type non-circular shaped fiber”, as used in the presentinvention, refers to fiber that may have cross section shape in waveform, and specifically, its shape is illustrated in FIG. 5.

The sound-absorbing material with excellent sound-absorbing performanceof the present invention can improves sound absorption coefficient andtransmission loss by forming large surface area and air layer, so as toinduce viscosity loss of incident sound energy. Further, it makeslight-weight design thereof possible since it can provide excellentsound-absorbing performance using reduced amount of fiber, and canimprove sound-absorbing performance by using binder fiber having reboundresilience, so as to maintain enough bonding strength between fibers andalso to maximize viscosity loss of sound energy transmitted to fiberstructure.

Accordingly, a sound-absorbing material having excellent sound-absorbingperformance, which can be used for improving noise insulationperformance of electric devices and the like using motor parts as wellas used through transport such as vehicle, train, ship, aircraft and thelike, and a method for manufacturing thereof can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a six-pointed star shaped non-circular shaped fiber, which iscontained in the sound-absorbing material according to a preferredembodiment of the present invention;

FIG. 2 is a 3-bar flat type non-circular shaped fiber, which iscontained in the sound-absorbing material according to a preferredembodiment of the present invention;

FIG. 3 is a 6-leaf type non-circular shaped fiber, which is contained inthe sound-absorbing material according to a preferred embodiment of thepresent invention;

FIG. 4 is a 8-leaf type non-circular shaped fiber, which is contained inthe sound-absorbing material according to a preferred embodiment of thepresent invention;

FIG. 5 is a wave type non-circular shaped fiber, which is contained inthe sound-absorbing material according to a preferred embodiment of thepresent invention;

FIG. 6 is a 8-leaf type non-circular shaped fiber, which is contained inthe sound-absorbing material according to a preferred embodiment of thepresent invention;

FIG. 7 is a 8-leaf type non-circular shaped fiber, which is contained inthe sound-absorbing material according to a preferred embodiment of thepresent invention; and

FIG. 8 is a drawing showing L and W of the 8-leaf type non-circularshaped fiber according to a preferred embodiment of the presentinvention as an example.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings and described below. While the invention will bedescribed in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention to those exemplary embodiments. On the contrary, the inventionis intended to cover not only the exemplary embodiments, but alsovarious alternatives, modifications, equivalents and other embodiments,which may be included within the spirit and scope of the invention asdefined by the appended claims.

As described above, since in the conventional sound-absorbing materialfor a fiber structure, surface density and thickness of fiber aggregateare increased in order to improve sound-absorbing performance and noiseinsulation performance by increasing porosity and sound wave dissipationroute, the vehicle becomes heavier thereby deteriorating fuelefficiency. Further, when low melting polyester binder fiber is used forthe conventional sound-absorbing material for a fiber structure, thefiber aggregate may be hardened. Thus, there was a problem that soundabsorption coefficient of low frequency is reduced since vibrationgenerated by sound wave propagation and transmitted to matrix structureis not fully attenuated.

Accordingly, the present invention provides a sound-absorbing materialwhich comprises: a non-circular shaped fiber satisfying the followingFormula 1; and a binder fiber which partly binds a plurality of thenon-circular shaped fibers, to find solutions for the above describedproblems.

$\begin{matrix}{1.5 \leq \frac{P}{\sqrt{4 \times \pi \times A}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

(A: Fiber cross sectional area (μm²), P: Circumference length of fibercross section (μm))

As such, sound absorption coefficient and transmission loss may beimproved by forming large surface area and air layer, so as to induceviscosity loss of incident sound energy. Further, -weight design thereofmay be obtained because excellent sound-absorbing performance may beobtained using reduced amount of fiber, and sound-absorbing performancemay be improved by using binder fiber having rebound resilience, so asto maintain enough binding strength between fiber and also to maximizeviscosity loss of sound energy transmitted to a fiber structure. Thus, asound-absorbing material having excellent sound-absorbing performance,which can be used for improving noise insulation performance of electricdevices and the like using motor parts as well as used through transportsuch as vehicle, train, ship, aircraft and the like, and a method formanufacturing thereof may be provided.

In general, when sound wave conflicts with a certain material, it maycause viscosity loss, thereby causing noise reduction while mechanicalenergy of the sound wave is converted to thermal energy. In order toreduce noise by increasing energy loss rate against sound waveintroduced to the fiber aggregate with the same weight, it isadvantageous to increase surface area of fiber where viscosity loss ofsound wave occurs.

The non-circular shaped fiber satisfy the η value of 1.5 or greater,calculated as

$\eta = \frac{P}{\sqrt{4 \times \pi \times A}}$

(A: Fiber cross sectional area (μm²), P: Circumference length of fibercross section (μm)), and it may secure greater surface area than thefiber used to the conventional sound-absorbing material for a fiberstructure, and improve sound absorption coefficient and transmissionloss. When the η value is less than 1.5, the fiber surface area may besmall. Thus, there is a problem that light-weight design thereof may beimpossible because a large amount of fiber needs to effectively embodysound-absorbing performance. The higher η value means the greater fibersurface area. Accordingly, more preferably, the non-circular shapedfiber used in the present invention may have the η value of 2.6 orgreater, and more preferably the value may be 3.0 to 7.0. If the η valueof the non-circular shaped fiber used in the present invention isgreater than 7.0, there may be a problem that production cost may beincreased due to increase of nozzle production cost, facilitiesreplacement related to cooling efficiency improvement, polymermodification for solidification rate improvement, productivity reductionand the like.

The non-circular shaped fiber of the present invention, which satisfiesthe η value of 1.5 or greater, may be a six-pointed star shape, 3-barflat type, 6-leaf type, 8-leaf type or wave type, or a combinationthereof. In the case of the wave type, when the η value satisfies 1.5 orgreater, specific shape such as the number of the curved point in thewave shape, length and width of the cross section and the like may vary.The number of the curved point in the wave shape means the point wherethe direction is changed to the length direction of the cross section,and for example, the number of the curved point of the wave typenon-circular shaped fiber in FIG. 5 is 4.

Specifically, FIG. 1 is six-pointed star shape non-circular shaped fiberaccording to a preferred embodiment of the present invention, and its ηvalue is 1.51, and FIG. 2 is 3-bar flat type non-circular shaped fiberaccording to a preferred embodiment of the present invention, and its ηvalue is 1.60. Further, FIG. 3 is 6-leaf type non-circular shaped fiberaccording to a preferred embodiment of the present invention, and its ηvalue is 1.93, FIG. 4 is 8-leaf type non-circular shaped fiber accordingto a preferred embodiment of the present invention, and its η value is2.50, FIG. 5 is wave type non-circular shaped fiber according to apreferred embodiment of the present invention, and its η value is 2.55,FIG. 6 is 8-leaf type non-circular shaped fiber according to a preferredembodiment of the present invention, and its η value is 2.8, and FIG. 7is 8-leaf type non-circular shaped fiber according to a preferredembodiment of the present invention, and its 11 value is 3.2.

The η value of a general circular type fiber with circular cross sectionis 1.0, and its sound absorption coefficient and transmission loss aresignificantly reduced because its surface area is not large enough (seeComparative Example 1), and although the non-circular shaped fiber are asix-pointed star shape, 3-bar flat type, 6-leaf type, 8-leaf type orwave type, if the η value does not satisfy 1.5 or greater, the surfacearea which can generate viscosity loss of the sound energy is notenough. Accordingly, those are not suitable as the non-circular shapedfiber used for the sound-absorbing material of the present invention(see Comparative Examples 2 to 5).

More preferably, the non-circular shaped fiber used in the presentinvention may have the L/W value of 2 to 3. L is the abbreviation forLength which is vertical length of fiber, and W is the abbreviation forWidth which is length against horizontal direction connecting betweenangular points. Specifically, FIG. 8 shows L and W values of the 8-leaftype non-circular shaped fiber. In the case of the cross section of the8-leaf type non-circular shaped fiber, when the longer direction iscalled vertical length, the length may be expressed as L, and in the 3shorter shape, the distance between angular points may be expressed asW.

Further, the non-circular shaped fiber used in the present invention mayhave 6 to 8 angular points more preferably, but it is not limited to theL/W or the number of the angular point. The non-circular shaped fiberwhich satisfies the η value of 1.5 or greater may be preferred.

Length of the non-circular shaped fiber may be 35 to 65 mm. When it isless than 35 mm, it may be difficult to form and produce fiber aggregatedue to wide gap between the fibers, and sound-absorbing and noiseinsulation performance may be reduced due to excess porosity. When it isover 65 mm, porosity may be reduced due to too narrow gap between thefibers, thereby reducing sound absorption coefficient. Further, finenessof the non-circular shaped fiber may be 1.0 to 7.0 De, and it may bemore effective to sound-absorbing performance as fineness becomes lower.When the fineness of the non-circular shaped fiber is less than 1.0 De,there may be a problem to control the optimum shape of the targetedcross section, and when it is greater than 7.0 De (denier), there may bea difficulty on non-woven fiber manufacturing process and a problem ofreduction of sound-absorbing performance when it is manufactured as thefiber aggregate.

The material of the non-circular shaped fiber included in thesound-absorbing material of the present invention may be preferablypolyethylene terephthalate (PET), but not particularly limited thereto.Polypropylene (PP), rayon, and any polymer that may be spun in fiberform may be used preferably as a sound-absorbing material.

Further, the sound-absorbing material of the present invention containsbinder fiber which partly binds a plurality of the non-circular shapedfibers.

The binder fiber may be any binder fiber which is generally used whenmanufacturing fiber structure, and it may be used in the form of powderas well as fiber, and more particularly, it may contain low melting (LM)elastomer. The elastomer generally refers to a polymer material havingexcellent elasticity such as rubbers, and i.e., it means a polymerhaving a characteristic that stretches when it is pulled by externalforce, and it is back to the original length when the external force isremoved. The preferable LM elastomer used in the present invention mayhave elastic recovery modulus of 50 to 80%. When elastic recoverymodulus is less than 50%, the fiber aggregate is hardened, andsound-absorbing performance may be reduced due to short flexibility.When it is greater than 80%, there may be problems that processabilitymay be reduced when manufacturing the fiber aggregate, as well asproduction cost of the polymer itself may be increased.

In the past, after the binder fiber was melted down and bound majorfiber together, the fiber aggregate was hardened such that there was aproblem that sound absorption coefficient was reduced because vibrationgenerated by sound wave propagation and transmitted to matrix structurewas not fully attenuated. However, in the present invention, reboundresilience rate (ASTM D 3574) of fiber structure is increased up to 50to 80% by containing a LM elastomer having elastic recovery modulus of50 to 80% in the binder fiber of the fiber aggregate, and attenuationcapability for the vibration which is ultimately transmitted inside thematrix is improved, and thus sound absorption coefficient andtransmission loss may be improved.

The LM elastomer may be a polyester-based polymer, a polyamide-basedpolymer, a polystyrene-based polymer, a polyvinylchloride-based polymeror polyurethane-based polymer, or combinations thereof

Further, more preferably, the LM elastomer may be manufactured byesterification and polymerization steps using dimethylterephthalate(DMT) and dimethyl isophthalate(DMI), or terephthalicacid(TPA) and isophthalic acid(IPA) as an acid ingredient(Diacid); and1,4-butanediol(1,4-BD) and polytetramethyleneglycol(PTMG) as a diolingredient (Diol).

The acid ingredient (Diacid) uses dimethyl terephthalate (DMT) anddimethyl isophthalate (DMI), or terephthalic acid (TPA) and isophthalicacid (IPA). The dimethyl terephthalate (DMT) and terephthalic acid (TPA)form a crystal region by reacting with the diol ingredient, and thedimethyl isophthalate (DMI) and isophthalic acid (IPA) form anon-crystal region by reacting with the diol ingredient, therebyproviding low melting function and elasticity.

Mixing ratio of dimethyl terephthalate (DMT) and dimethyl isophthalate(DMI) may be a molar ratio of 0.65˜0.80:0.2˜0.35, preferably, and mixingratio of terephthalic acid (TPA) and isophthalic acid (IPA) also may bemolar ratio of 0.65˜0.80:0.2˜0.35, preferably. When the molar ratio ofdimethyl isophthalate (DMI) and isophthalic acid (IPA) is less than theabove described range, elastic recovery modulus may be deteriorated, andthe low melting function may not be expressed. When the molar ratio ofdimethyl isophthalate (DMI) and isophthalic acid (IPA) is greater thanthe above described range, physical properties may be deteriorated.

The diol ingredient (Diol) uses 1,4-butanediol (1,4-BD),polytetramethyleneglycol(PTMG), and 1,4-butanediol forms a crystalregion by reacting with acid ingredient andpolytetramethyleneglycol(PTMG) forms a non-crystal region by reactingwith acid ingredient, thereby providing low-melting function andelasticity.

Mixing ratio of the 1,4-butanediol (1,4-BD), polytetramethyleneglycol(PTMG may be a molar ratio of 0.85˜0.95:0.05˜0.15, preferably. When themolar ratio of polytetramethyleneglycol (PTMG) is less than the abovedescribed range, elastic recovery modulus may be deteriorated, and thelow-melting function may not be expressed. When the molar ratio ofpolytetramethyleneglycol (PTMG) is greater than the above describedrange, physical properties may be deteriorated. 1,4-butanediol (1,4-BD)may be used as a mixture with ethyleneglycol (EG) within the abovedescribed range.

Further, molecular weight of the polytetramethyleneglycol (PTMG) may bein a range of 1500 to 2000, preferably. When the molecular weight of thepolytetramethyleneglycol (PTMG) is out of the said range, elasticity andphysical properties of the LM elastomer to be manufactured may not besuitable for use.

The acid ingredient and the diol ingredient may be mixed at molar ratioof 0.9˜1.1:0.9˜1.1 and polymerized, preferably. When any one ingredientof the acid ingredient and the diol ingredient is excessively mixed, itis not used to be polymerized and is discarded. Accordingly, it ispreferred to mix the acid ingredient and the diol ingredient at similaramounts.

As described above, the LM elastomer manufactured from dimethylterephthalate(DMT), dimethyl isophthalate(DMI) as the acidingredient(Diacid) and 1,4-butanediol(1,4-BD),polytetramethyleneglycol(PTMG) as the diol ingredient(Diol) ismanufactured to have melting point of 150˜180° C. and elastic recoverymodulus of 50˜80%.

Further, the binder fiber of the sound-absorbing material of the presentinvention may be a conjugated fiber which is conjugate-spun by using theLM elastomer as one component. More preferably, it may be sheath-coretype or side by side type conjugated fiber. When the sheath-core typeconjugated fiber is formed, the LM elastomer may be used as a sheathingredient, and general polyester may be used as a core ingredient. Thegeneral polyester reduces production cost and functions as fibersupporter, and the LM elastomer allows to express elasticity and lowmelting function.

Preferably, the binder fiber may be manufactured by using the LMelastomer and the general polyester at weight ratio of 40:60˜60:40. Whenthe LM elastomer is contained at weight ratio of less than 40,elasticity and low melting function may be deteriorated, and when it iscontained at weight ratio of over 60, there is a problem of increase ofproduction cost.

The sound-absorbing material may contain the non-circular shaped fiberof 50 to 80 wt % based on the total weight of the sound-absorbingmaterial and the binder fiber of 20 to 50 wt % based on the total weightof the sound-absorbing material. When the content of the non-circularshaped fiber is less than 50 wt %, it may be difficult to embody theoptimal sound-absorbing and noise insulation performances due to reducedfiber surface area, but when the content of the non-circular shapedfiber is greater than 80 wt %, the content of the binder fiber becomesless than 20 wt %, relatively, and it may be difficult to maintainenough binding strength between the fiber. Thus, it may be difficult toform the sound-absorbing material to a certain shape and the vibration,which is generated from sound wave propagation and transmitted to thematrix structure, is not fully attenuated because the matrix structureis not strong, such that low frequency sound absorption coefficient maybe reduced. As the content of the binder fiber is increased to 20 to 50wt %, rebound elasticity modulus (ASTM D 3574) increases up to 50 to80%.

This fiber structure with polymorphic cross section having excellentsound-absorbing performance is manufactured by a method formanufacturing a sound-absorbing material that comprises forming fiberaggregate in the nonwoven fabric fabric form. The fiber aggregatecomprises: a non-circular shaped fiber satisfying the following Formula1; and binder fiber which partly binds a plurality of the non-circularshaped fibers.

$\begin{matrix}{1.5 \leq \frac{P}{\sqrt{4 \times \pi \times A}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

(A: Fiber cross sectional area (μm²), P: Circumference length of fibercross section (μm))

The sound-absorbing material may be manufactured by forming the fiberaggregate containing the non-circular shaped fiber and the binder fiberin the non-woven form having a certain surface density by generalmanufacturing processes for a fiber structure sound-absorbing materialsuch as needle punching process or thermal adhesion process and thelike. Hereinafter, detailed description about the above-describednon-circular shaped fiber and the binder fiber, which are identicallyapplied to the method for manufacturing the sound-absorbing material ofthe present invention will be omitted.

EXAMPLES

The following examples illustrate the invention and are not intended tolimit the same.

Example 1

Polyester-based 8-leaf type (FIG. 4, η=2.5) non-circular shaped fiber(6.5 De, 61 mm, strength 5.8 g/D, elongation rate 40%, crimp number14.2/inch) and sheath-core type conjugated fiber containingpolyester-based LM elastomer as binder fiber were mixed at weight ratioof 8:2, the mixture was physically broken down through needle punchingprocess after controlling weight constantly, and then non-woven typefiber aggregate having thickness of 20 mm and surface density of 1600g/m² was manufactured through a general thermal adhesion process.Rebound resilience of the manufactured sound-absorbing material was 55%.

The sheath-core type conjugated fiber containing polyester-based LMelastomer as binder fiber contained polyester-based LM elastomer as asheath ingredient, and the polyester-based LM elastomer used a mixtureof terephthalic acid of 75 mole % and isophthalic acid of 25 mole % asan acid ingredient and a mixture of polytetramethyleneglycol of 8.0 mole% and 1,4-butanediol of 92.0 mole % as a diol ingredient, andmanufactured by mixing and polymerizing the acid ingredient and the diolingredient at molar ratio of 1:1. The LM elastomer manufactured asmentioned above has melting point of 50° C., intrinsic viscosity of 1.4and elastic recovery modulus of 80%. As the core ingredient,polyethylene terephthalate(PET) having melting point of 260° C. andintrinsic viscosity of 0.65 was used, and conjugated fiber havingfineness of 6 D, strength of 3.0 g/D, elongation rate of 80%, crimpnumber of 12/inch and fiber length of 64 mm was manufactured by spinningusing a conjugate spinning nozzle, which can conjugate spin thepolyester-based LM elastomer and the general PET at spinning temperatureof 275° C. and winding speed of 1,000 mm/min, elongated by 3.3 folds at77° C., and finally heated at 140° C.

Example 2

The procedure of Example 1 was repeated except for manufacturingnon-woven type fiber structure having thickness of 20 mm, surfacedensity of 1200 g/m².

Example 3

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using six-pointed star shaped (FIG. 1, η=1.51)non-circular shaped fiber.

Example 4

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using 3-bar flat type (FIG. 2, η=1.60)non-circular shaped fiber.

Example 5

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using 6-leaf type (FIG. 3, η=1.93) non-circularshaped fiber.

Example 6

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using wave type (FIG. 5, η=2.55) non-circularshaped fiber.

Example 7

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using 8-leaf type (FIG. 6, η=2.8) non-circularshaped fiber non-circular shaped fiber.

Example 8

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using 8-leaf type (FIG. 7, η=3.2) non-circularshaped fiber non-circular shaped fiber.

Example 9

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using low melting PET fiber as binder fiber.Rebound resilience of the manufactured sound-absorbing material was 30%.

Comparative Example 1

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using circular (η=1.0) shaped fiber.

Comparative Example 2

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using five-pointed star shape (η=1.30)non-circular shaped fiber.

Comparative Example 3

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using wave type (η=1.42) non-circular shapedfiber.

Comparative Example 4

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using Y type (η=1.26) non-circular shapedfiber.

Comparative Example 5

The procedure of Example 1 was repeated except for manufacturing asound-absorbing material using six-pointed star shape (η=1.41)non-circular shaped fiber.

Test Example

In order to evaluate sound-absorbing and noise insulation performancesof the sound-absorbing materials manufactured according to Examples 1 to9 and Comparative Examples 1 to 5, the materials were tested as thefollowing measuring methods, and the results were shown in Tables 1 and2.

1. Sound Absorption Coefficient

In order to measure sound absorption coefficient, 3 specimens applicableto ISO R 354, Alpha Cabin method were manufactured, respectively,sound-absorbing coefficients were measured and the mean of the measuredsound-absorbing coefficients were shown in Table 1.

2. Transmission Loss

In order to measure noise insulation effect, 3 specimens applicable to atransmission loss coefficient evaluating device (APAMAT-II) weremanufactured, respectively, insertion loss was measured, and the meanvalue of the measured insertion loss was shown in Table 2.

3. Elastic Recovery Modulus

A dumbbell shape specimen having thickness of 2 mm and length of 10 cmwas elongated 200% at a rate of 200%/min using Instron, waited for 5sec, and the elongated length after recovered at the same rate wasmeasured, and then elastic recovery modulus was calculated by thefollowing Formula.

${{Elasticity}\mspace{14mu} {Recovery}\mspace{14mu} {Rate}\mspace{14mu} (\%)} = {\frac{20 - \left( {L - 10} \right)}{20} \times 100\mspace{14mu} \left( {L\text{:}\mspace{14mu} {Elongated}\mspace{14mu} {Length}} \right)}$

4. Rebound Resilience Rate (Ball Rebound)

After dropping a metal ball from a certain height to a test specimen,the height of the rebound ball was measured (JIS K-6301, unit: %). Testspecimen was made into a square having a side length of 50 mm or greaterand thickness of 50 mm or greater, and a steel ball having weight of 16g and diameter of 16 mm was dropped from a height of 500 mm to the testspecimen, and then the maximum rebound height was measured. Then, foreach 3 test specimens, the rebound value was measured at least 3 timesin a raw within 1 min, and the median value was used as reboundresilience rate (%).

TABLE 1 Sound absorption coefficient per frequency (Hz) 1000 Hz 2000 Hz3150 Hz 5000 Hz Example 1 0.67 0.75 0.84 0.96 Example 2 0.54 0.63 0.770.85 Example 3 0.62 0.67 0.78 0.88 Example 4 0.59 0.71 0.81 0.90 Example5 0.62 0.69 0.80 0.90 Example 6 0.66 0.77 0.85 0.97 Example 7 0.67 0.780.89 0.99 Example 8 0.68 0.79 0.91 1.00 Example 9 0.50 0.70 0.79 0.89Comparative 0.51 0.61 0.74 0.83 Example 1 Comparative 0.57 0.65 0.750.86 Example 2 Comparative 0.57 0.62 0.76 0.86 Example 3 Comparative0.56 0.64 0.75 0.85 Example 4 Comparative 0.61 0.65 0.75 0.86 Example 5

TABLE 2 Transmission loss (dB) per frequency (Hz) 1000 Hz 2000 Hz 3150Hz 5000 Hz Example 1 25 27 35 43 Example 2 23 24 32 41 Example 3 22 2532 40 Example 4 24 25 33 41 Example 5 24 26 33 41 Example 6 25 27 35 44Example 7 26 28 36 45 Example 8 27 30 38 47 Example 9 21 24 31 40Comparative 22 23 31 40 Example 1 Comparative 21 24 31 40 Example 2Comparative 22 24 32 41 Example 3 Comparative 21 24 31 40 Example 4Comparative 22 24 32 40 Example 5

As shown in Tables 1 and 2, as comparing the results of measuringsound-absorbing and noise insulation performances in Examples 1 to 9 andComparative Examples 1 to 5, it was found that sound-absorbing and noiseinsulation performances of the fiber aggregate were improved as thefiber surface areas were increased.

Specifically, as comparing the result of measuring performances ofExample 2 and Comparative Example 1, it was found that thesound-absorbing material using the non-circular shaped fiber of thepresent invention had better sound-absorbing and noise insulationperformances than the fiber sound-absorbing material using fiber withcircular cross section generally used, despite the reduced surfacedensity of the fiber aggregate, and therefore, light-weight designthereof is possible by using reduced amount of fiber.

It is found that Examples 1 to 9 satisfying the η value of 1.5 orgreater had improved sound absorption coefficient and transmission lossthan Comparative Examples 1 to 5 having the η value of less than 1.5. Itwas found that Comparative Example 5 having the value of less than 1.5also had low effect on sound absorption coefficient and transmissionloss due to small surface area, although six-pointed star shapenon-circular shaped fiber was used.

Further, as comparing the results of measuring performances of Example 9using the low melting PET fiber as binder fiber and Examples 1 to 8using the low melting elastomer, it was found that flexible structurehaving rebound elasticity rate of 55% was obtained by using low meltingelastomer as binder fiber, and sound-absorbing performance was improvedby improved attenuation capability of the vibration transmitted to thematrix structure.

What is claimed is:
 1. A method for manufacturing a sound-absorbing material, comprising forming a fiber aggregate in a nonwoven fabric form, wherein the fiber aggregate comprises: a non-circular shaped fiber satisfying the following Formula 1; and a binder fiber that partly binds a plurality of the non-circular shaped fibers, $\begin{matrix} {1.5 \leq \frac{P}{\sqrt{4 \times \pi \times A}}} & {{Formula}\mspace{14mu} 1} \end{matrix}$ wherein A is a fiber cross sectional area (μm²), P is a circumference length of fiber cross section (μm).
 2. The method for manufacturing a sound-absorbing material of claim 1, wherein the sound-absorbing material is manufactured by using the non-circular shaped fiber satisfying the value of the Formula 1 of 2.6 or greater.
 3. The method for manufacturing a sound-absorbing material of claim 1, wherein the non-circular shaped fiber is at least one selected from the group consisting of six-pointed star shape, 3-bar flat type, 6-leaf type, 8-leaf type and wave type.
 4. The method for manufacturing a sound-absorbing material of claim 1, wherein the non-circular shaped fiber is 35 to 65 mm in length.
 5. The method for manufacturing a sound-absorbing material of claim 1, wherein the binder fiber comprises a low melting (LM) elastomer having elastic recovery modulus of 50 to 80%.
 6. The method for manufacturing a sound-absorbing material of claim 5, wherein the binder fiber is a conjugated fiber which is conjugate-spun by using the LM elastomer as one component.
 7. The method for manufacturing a sound-absorbing material of claim 5, wherein the LM elastomer is at least one selected from the group consisting of a polyester-based polymer, a polyamide-based polymer, a polystyrene-based polymer, a polyvinylchloride-based polymer and a polyurethane-based polymer.
 8. The method for manufacturing a sound-absorbing material of claim 5, wherein the LM elastomer is manufactured by esterification and polymerization steps using dimethyl terephthalate(DMT) and dimethyl isophthalate(DMI) or terephthalic acid(TPA) and isophthalic acid(IPA) as an acid ingredient(Diacid), and 1,4-butanediol(1,4-BD), polytetramethyleneglycol(PTMG) as a diol ingredient (Diol).
 9. The method for manufacturing a sound-absorbing material of claim 1, wherein the sound-absorbing material is manufactured by using the non-circular shaped fiber of 50 to 80 wt % based on the total weight of the sound-absorbing material and the binder fiber of 20 to 50 wt % based on the total weight of the sound-absorbing material.
 10. The method for manufacturing a sound-absorbing material of claim 1, wherein the non-circular shaped fiber satisfies the value of the Formula 1 of 3.0 or greater.
 11. A sound-absorbing material, comprising: a non-circular shaped fiber satisfying the following Formula 1; and a binder fiber that partly binds a plurality of the non-circular shaped fibers, $\begin{matrix} {1.5 \leq \frac{P}{\sqrt{4 \times \pi \times A}}} & {{Formula}\mspace{14mu} 1} \end{matrix}$ wherein A is a Fiber cross sectional area (μm²),), P is a Circumference length of fiber cross section (μm).
 12. The sound-absorbing material of claim 11, wherein the non-circular shaped fiber satisfies the value of the Formula 1 of 2.6 or greater.
 13. The sound-absorbing material of claim 11, wherein the non-circular shaped fiber is at least one selected from the group consisting of six-pointed star shape, 3-bar flat type, 6-leaf type, 8-leaf type and wave type.
 14. The sound-absorbing material of claim 11, wherein the non-circular shaped fiber is 35 to 65 mm in length.
 15. The sound-absorbing material of claim 11, wherein the non-circular shaped fiber is 1.0 to 7.0 De in fineness.
 16. The sound-absorbing material of claim 11, wherein the binder fiber comprises a low melting (LM) elastomer having elastic recovery modulus of 50 to 80%.
 17. The sound-absorbing material of claim 16, wherein the binder fiber is conjugated fiber which is conjugate-spun by using the LM elastomer as one component.
 18. The sound-absorbing material of claim 16, wherein the LM elastomer is at least one selected from the group consisting of a polyester-based polymer, a polyamide-based polymer and a polyurethane-based polymer.
 19. The sound-absorbing material of claim 11, which comprises the non-circular shaped fiber of 50 to 80 wt % based on the total weight of the sound-absorbing material and the binder fiber of 20 to 50 wt % based on the total weight of the sound-absorbing material.
 20. The sound-absorbing material of claim 11, wherein the non-circular shaped fiber satisfies the value of the Formula 1 of 3.0 or greater. 